TITLE: GCN CIRCULAR NUMBER: 45934 SUBJECT: GRB 261011A: Swift-XRT refined Analysis DATE: 26/10/13 07:14:45 GMT FROM: Phil Evans at U of Leicester A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J.J. DeLaunay (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.2 ks of XRT data for GRB 261011A, from 301 s to 28.0 ks after the trigger. The data comprise 1.2 ks in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 1938 s of PC mode data and 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 21.89722, -21.56052 which is equivalent to: RA (J2000): 01h 27m 35.33s Dec(J2000): -21d 33' 37.9" with an uncertainty of 2.9 arcsec (radius, 90% confidence). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=4.1 (+/-0.6). At T+362 s the decay flattens to an alpha of 1.68 (+0.11, -0.10) before breaking again at T+792 s to a final decay with index alpha=1.26 (+0.06, -0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+/-0.05). The best-fitting absorption column is 7.7 (+1.7, -1.6) x 10^20 cm^-2, in excess of the Galactic value of 0.0 x 10^00 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 7.7 (+1.7, -1.6) x 10^20 cm^-2 Galactic foreground: 1.5 x 10^20 cm^-2 Excess significance: 6.4 sigma Photon index: 1.80 (+/-0.05) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01516664. This circular is an official product of the Swift-XRT team.